In the low-pressure turbine stages of turbojets, parts are assembled to one another by means of annular flanges pressed against one another and fastened together by bolts which pass through orifices in the annular flanges, these orifices being distributed regularly around the annular flanges.
Some such flanges are “festooned”, i.e. their through orifices for fastening bolts are formed in solid portions which are separated from one another by notches giving such annular flanges a “festooned” shape, in other words a shape that is crenellated with edges that are rounded or rectangular.
For a low-pressure turbine of a turbojet, the various parts are stacked vertically on one another, and they are then fastened together by means of bolts which are passed blind through the orifices in the annular flanges. It can thus happen that a festooned flange is angularly offset relative to the other flanges by half of the pitch between the through orifices for passing the fastening bolts, and under such circumstances, the bolts threaded through the orifices in the other flanges pass through the notches in the offset festooned flange, and not through the orifices provided in the solid portions of that flange. Under such circumstances, the offset flange is not securely fastened to the other flanges since it is merely clamped axially between the other flanges, and it might move angularly or radially in the event of the fastening bolts loosening or under centrifugal forces.
No known means are provided to ensure proper angular positioning of annular fastening flanges, other than the care taken by operatives performing assembly, and no means are provided for warning operatives that angular positioning is bad.